The need to protect internal combustion engines from damaging or destructive operating conditions is well known. Such need can become particularly important in the case of high performance engines which not only themselves may be costly and expensive to maintain, repair or replace, but which may also be used to operate sophisticated and costly equipment, the downtime and repair of which is preferably kept to a minimum.
Various devices or systems for the protection of internal combustion engines are known in the prior art. Some of such devices are essentially dedicated to a single task; for example, the tilt detector disclosed in U.S. Pat. No. 3,882,957 (Fritz) entitled "Vehicle Roll-Over Protection Device", granted on May 13, 1975. Here, a tilt detecting apparatus was designed to effect vehicle engine shutdown if the vehicle rolled over or tilted more than a predetermined amount.
Other known sensing or detecting devices which may be used to monitor and sense engine operating conditions or its immediate environment include devices for monitoring and sensing conditions or parameters such as engine or other temperatures, oil pressures, rpms, water, fuel (fuel leakage), fluid levels (water or other coolant), fire, and so forth. Signalling from such devices may readily be utilized to effect engine shutdown based upon the presence or absence of a signal having a magnitude above or below a predetermined threshold value.
In contrast to devices or systems dedicated to a single task, some known engine protection devices or systems are designed to effect engine shutdown if any one of more than one of the previously described devices or systems, operating concurrently to control a particular engine, produces a signal that dictates engine shutdown. An example of such a system is disclosed in U.S. Pat. No. 4,429,670 (Ulanet) entitled "Engine Protection Systems", granted on Feb. 7, 1984. As described in the patent to Ulanet, his system includes visual and audible signals responsive to operative conditions of at least a coolant level, engine temperatures, high and low oil pressures, and air intake pressures. If an operative condition endures for a period of time determined by the passage of current through a circuit breaker, engine shutdown is effected by tripping current to the solenoid of an engine fuel valve.
The ability of an engine protection system to respond to more than one sensed operating or environmental condition is a desirable feature. In practical terms, any one of such conditions may represent a threat to an engine or its associated equipment. To afford protection against only one condition is limiting and may be considered inadequate for many applications. However, known systems that are designed to respond to any one of a plurality of sensed operating conditions generally fail to distinguish any one threatening condition from the next, and generally fail to recognize that the control and response of the system may preferably or advantageously depending upon the character of particular threatening conditions. For example, in the case of the system disclosed by Ulanet, there is essentially a series connection of switches, the opening of any one of which will initiate the same control regime leading up to engine shutdown, viz. current through a circuit breaker which, if not manually overridden and allowed to endure for a predetermined period of time, will ultimately trip the breaker and current to a fuel valve as noted above. The timing of engine shutdown control is essentially fixed.